The photoreceptor cell is affected by a variety of genetic diseases and trauma. Both its outer segment and the synaptic terminal respond to these pathological conditions. This proposal examines the plasticity of the photoreceptor ribbon synapse and its ability to regenerate and has the following aims: (1) to localize the calcium channels in the rod and cone photoreceptor; (2) to test whether synaptic plasticity is controlled by calcium signals and vesicle recycling; and (3) to examine for inhibitory interaction between adult neurons that may limit regeneration and recovery of synaptic function. Confocal laser scanning and electron microscopy will be used on isolated photoreceptors in conjunction with fluorescent dihydropyridines, inhibitors of protein synthesis, and markers of cell organelles, to examine structural plasticity. Creation of groups of retinal neurons in culture by micromanipulation with optical tweezers, followed by conventional and video time-lapse microscopy, will test potential repulsive and attractant cell-mediated forces during regeneration. The projects explore possible mechanisms involved in axonal retraction and neuritic outgrowth seen in retinal detachment and retinitis pigmentosa, respectively. Understanding the cell biology of the ribbon synapse may help restore or preserve normal neurotransmission in retinal disease.